Solid propellant formulation continuing fluoro-amino compounds and polymers

ABSTRACT

1. A high-energy composite which on ignition burns at a controlled rate at a specific impulse in the range of 260 to 300 seconds, comprising 2 to 15 wt. percent boron, 5 to 25 wt. percent of a CNF2 oxidizer selected from the group consisting of tetrakis (difluoramino) butane and tetrakis (difluoramino) tetrahydrofuran, 40 to 60 wt. percent of an oxygen oxidizer selected from the group consisting of nitronium perchlorate, hydrazinium nitroformate, hexanitroethane and ammonium perchlorate, and 5 to 30 wt. percent of a solid polymeric binder having the composition of polybutadiene (N2F4) adducts represented by the recurring unit composition in which y represents 1.3 to 2 NF2 groups per recurring unit, the boron being in a 1:1 atomic ratio to fluorine in the composite to form BOF as a main combustion product.

United States Patent 1191 Bieber et al.

[ Dec. 31, 1974 SOLID PROPELLANT FORMULATION CONTINUING FLUORO-AMINO COMPOUNDS AND POLYMERS of NJ.

[73] Assignee: Exxon Research & Engineering Co.,

Linden, NJ.

[22] Filed: May 17, 1961 211 App]. No.: 111,131

Related U.S. Application Data [63] Continuation-in-part of Ser. No. 77,470, Dec. 21,

1960, Pat. No. 3,535,173.

[52] U.S. Cl l49/19.3, 149/20, 149/19.9, 149/22, 149/36, 149/75, 149/89 [51] Int. Cl C06d /06 [58] Field of Search 149/19, 20, 22, 36, 44 149/89, 75, 71

[56] References Cited UNITED STATES PATENTS 3,369,943 2/1968 Longwellet a1. 149/18 3,425,922 2/ 1969 Guthrie 149/19 X Primary Examiner-Benjamin R. Padgett Attorney, Agent, or Firml-1enry Berk EXEMPLARY CLAIM l. A high-energy composite which on ignition burns at a controlled rate at a specific impulse in the range of 260 to 300 seconds, comprising 2 to wt. percent boron, 5 to wt. percent of a CNF oxidizer selected from the group consisting of tetrakis (difluoramino) butane and tetrakis (difluoramino) tetrahydrofuran, to wt. percent of an oxygen oxidizer selected from the group consisting of nitronium perchlorate, hydrazinium nitroformate, hexanitroethane and ammonium perchlorate, and 5 to 30 wt. percent of a solid polymeric binder having the composition of polybutadiene (N F adducts represented by the recurring unit composition [C H (NF )4] in which y represents 1.3 to 2 NE groups per recurring unit, the boron being in a 1:1 atomic ratio to fluorine in the composite to form BOF as a main combustion product.

5 Claims, N0 Drawings SOLID PROPELLANT FORMULATION CONTINUING FLUORO-AMINO COMPOUNDS AND POLYMERS This application is a continuation-in-part of U.S. application Ser. No. 77,470, filed Dec. 21, 1960 by L. Spenadel and H. Bieber, now U.S. Pat. no. 3,535,173, and which discloses the use ofliquid compounds having a high proportion of NF /C groups to plasticize solid polymeric binders containing NF groups to form plastisols. These solid and liquid compounds are termed CNF compounds for brevity, indicating that they contain NF groups linked to carbon atoms.

This invention relates to solid propellants formulated from a powdered boron fuel, a solid oxygen-oxidizer, a high-energy binder containing NF groups, and a plasticizer containing NF groups, these ingredients being proportioned to obtain satisfactory burning rates at high impulse levels.

Work on combustion of propellants containing the solid and liquid compounds of high NF IC contents has shown that these propellants have excessively fast burning rates, especially those containing high amounts of the CNF liquid plasticizers. For example, a propellant containing boron, ammonium perchlorate as oxygen-oxidizer, CNF polymer as binder with the liquid C H (NF as plasticizer has a burning rate of inches per second at 500 psi. when these ingredients are compounded to make the propellants NF content 45 wt. percent. The impulse (Isp) of this propellant is only 260.

Studies show that propellant compositions having a high NF content have high burning rate when balanced to form BF or HF (with no B present). Such compositions can have Isp values higher than 260, but 35 not at realistic burning rates. At the high burning rates there is a tendency to detonation. In such systems the oxygen-supplying oxidizer is present in a proportion to burn the carbon, e.g., to form CO. The boron is reacted with fluorine to form BF H is either burned to HF or discharged as H In accordance with the present invention, the propellants containing boron, oxygen-oxidizer, and CNF compounds are balanced to form BOF. This enables achievement of lsp values in the range of about 265 to 300 with desirable burning rates of about 0.5 to 2.0 inches per second.

There is a marked advantage for the system balanced to BOF formation when compared to those balanced to BF; formation on a constant lsp basis (thrust in pounds force per second per pound of propellant).

Basically, to obtain a propellant balanced for BOF formation, less CNF liquid is required as fluorineoxidizer and plasticizer and the resultant propellant has an NF content preferably less than wt. percent. Enough oxygen-oxidizer is used to supply 0 for BOF and to burn carbon to CO. The binder and CNF liquid are used in a proportion to supply F for BOF. The binder is used in sufficient amount to give structural strength of the solid propellant grain, e.g., usually 10 to 30 wt. percent of the composite.

The CNF solids and liquids are recent in their development. That is why burning rate effects of these materials compounded with fuels and other oxidizers have not been understood fully hitherto.

In a propulsion system, thrust is the reaction force produced by expelling particles of high velocity from a combustion zone through a nozzle opening, the particles being gaseous, solid, liquid or even bundles of en ergy. In general, these particles are collectively termed gas or gaseous working fluid.

The specific impulse (Isp) is a measure of thrust and varies with temperature in the combustion chamber in which the propellant components of fuel and oxidizer undergo combustion. It is expressed usually as in terms of seconds.

Thrust of a system lasts only so long as working fluid is produced for expulsion and does not depend on total amount or density of propellant material. Therefore, another useful measure of performance is the relative boost velocity which is a function of density and of specific impulse of a propellant. The relative boost velocity (RBV) is evaluated with reference to a standard propellant.

In earlier studies, burning rates of propellants containing a CNF binder with a solid oxidizer such as perchlorate or nitroformate were found to rise rapidly with increased CNF liquid plasticizer added. These systems were balanced to form HF gas product. Next, it was found that boron powder could be added to such system in proportions to form BF or BOF combustion products. The BOF system was then found to have a 30 to 50 percent faster burning rate than the HF or BF forming systems at the same NF level. However, the BOF system has an lsp above 270 at a 20 to 28 percent NF level, whereas the HF and BF systems have an lsp in the range of 220 to 250 at this NF level. In the 265 to 300 specific impulse range the HF/BF systems are characterized by extremely rapid and unstable burning. The HF/BF systems have to contain to percent NF to obtain this higher impulse. Thus, the BOF- forming systems were found to be preferred for high impulse and controlled burning. Since one might expect that burning rates increase with increasing energy content (higher lsp), the achievement of low burning rates at the 270 Isp level (by formulating to BQflis quite surprising and novel.

Formulation of propellants containing CNF compounds with oxygen oxidizers and boron-supplying fuel to produce BOF rather than BF and HF is advantageous for better boost performance as well as for better burning rate and higher lsp. The addition of boron increases density, which helps the boost velocity.

Whereas in fluorine oxidizing systems balanced to HF/BF the boron is added to combine with fluorine in excess of the hydrogen, in the present disclosed systems of improved performance the fluorine available for reaction is lowered as the proportion of boron and oxygen from the oxygen oxidizer is increased.

The solid propellants or hot gas-generating composites of interest generally contain fuel constituents such as carbon hydrogen, and boron, fluorine oxidizing constituents in the CNF ingredients and oxygen oxidizing constituents in ingredients containing nitro groups, perchlorate groups, or both nitro and perchlorate groups. The carbon and hydrogen constituents may come from a hydrocarbon moiety of the oxidizer and from a binder ingredient which may also contain CNF nitro groups or both. The fuel, oxidizer, and binder ingredients may be intimately mixed and cast or otherwise shaped into a solid mass, called a grain, which is cemented or attached to a rocket case in its combustion chamber.

For testing purposes two types of systems were selected, one with a normal oxygen oxidizer, hydrazinium nitroformate, the other with a more energetic oxygen oxidizer, hexanitroethane. The systems compared were:

TABLE 1 Fuel -boron B Fluorine Oxidizer -tetrakis (NF butane C H (NF Oxygen Oxidizer -hydrazinium nitro- N H C(NO formatc hexanitroethang C2(NO2)B Binder -polybutad1ene (N F [g l'lrggN F zlgl adduct Among other potent oxygen oxidizers are bis (trinitroethyl) nitramine, nitroform, nitronium perchlorate, ammonium perchlorate, hydrazinium perchlorate, etc. Some of these are very reactive and have to be encapsulated in a compatible material such as aluminum or suitable resin. Generally, the oxygen oxidizers are solids and of relatively high density, e.g., about 1.6 to 2.2 g/cc.

The preferred binders are also energy suppliers in containing NF N or both kinds of groups. The polybutadiene-N F adducts suitable as binders are represented by the formulae [C H (NF or [C H (NF in which y represents about 1.3 to 2 and x is the number indicating the number of recurring units. Other binders may be made to contain more or fewer NF groups. Other high energy polymers are represented by polynitrourethane, polyvinyl furoate-N F adducts, nitrocellulose, etc. For balancing the compositions, lower energy polymers may be used in minor amounts, e.g., saturated or synthetic rubbers denoted generally by CH To achieve high impulse ratings in the range of 270 to 300, the high energy binder is preferably used in a proportion of about 10 to wt. percent. Enough of the binder is employed to obtain the lsp, Sec,

The systems formulated to contain less than 30 wt. percent NF and to form H -BOF products of combustion have higher impulses than those forcing HF+BF or H +BF combustion products even with increasing proportions of binder. Added binder in proportions of about 10 to 30 wt. percent results in less dissociation of the propellant particularly with a sufficiently low proportion of boron, e.g., 2 to 10 wt. percent. The high NF level systems have to contain more boron, are much hotter, and more dissociated.

The low NF level system which forms BOF combustion product has a distinctly higher boost velocity compared to the other systems throughout variations in proportions of binder from 0 to 30 wt. percent.

in the preferred formulations containing B as fuel the atomic ratio of B/F in the ingredients and products is 1:1. The O/C ratio is generally about 2:1 or in the range of 1.8:1 to 28:1 since 0 is needed to form BOF as well as to form CO.

Powered boron is preferably used as the fuel ingredient to form the BOF combustion product. However, other ingredients that supply boron may be used, e.g., hydrazine bis borane, (N H (BH denoted by the abbreviation HBB or related boranes.

Among other potent fluorine oxidizers are compounds such as tetrakis (NF tetrahydrofuran and other acyclic or cyclic compounds having at least 1 NF group per carbon atom, generally containing about three to six carbon atoms per molecule and preferably four to six carbon atoms per molecule. These compounds are beneficial in raising the lsp and in plasticizing potent binders which also contain NF groups and- /or nitro groups.

desired cohesion of the mixed ingredients into a solid or plastisol mixture that hardens to a solid even with a liquid CNF oxidizer-plasticizer admixed.

In preparing solid propellant grains from ingredients that contain the necessary fuel and oxidizing constituents, it is important to use methods that are safe and permit ease of handling.

The plastisols are mixtures of solid and liquid ingredients having adequately safe capabilities and which under conditions of mixing form a fluid or semi-fluid mass that becomes transformed into a solid gel having minimum rubbery properties. The rubbery mass obtained should have a tensile strength above 20 pounds per square inch and an elongation of over 10 percent, as minimum requirements of stiffness and elasticity.

After mixing the solid and liquid ingredients, the mixture can be cast or molded, then set by curing. The mixing, handling and curing may be carried out at moderate temperatures of about 20 to 60C.

If the gel or plastisol is on the soft side, various reinforcing fibrous materials may be admixed, e.g., aluminum wool, or fibers of polymers or of other fuel ingredients for adding rigidity. Stiffness is imparted by increasing the proportion of binder.

In general the mixtures contain the ingredients in the following proportions:

Examples of propellant compositions which produce BOF as the main F-containing product are the followmg:

tane and the oxygen oxidizer is hexanitroethane.

3. A high-energy composite as defined in claim 1 in which the CNF oxidizer is tetrakis (difluoramino) tet- TABLE 2 DENSITY MAIN COMPOSITION WT.7 GJCC. 1S1 RBV PRODUCTS CIHINFz, 10.24 1.85 289 1.1 BOF I B 11.59 CO 1 i NO CKL 48.17 HCl [C4HQ(NF2)2] 30.00 H +N C H (NF 21.49 1.74 292 1.07 BOF B 11.20 CO 11 C (NO)B 52.30 H 1 4 a( 2)21.r 15.00 2

C 11 (N1 6.01 1.71 287 1.05 BOF 1 B 1020 CO 111 C (NO 53.80 N [C 11 (NF 30.00 H;

C.H,(NF 13.52 1.76 278 1.03 BOF B 9.71 CO [V N H C(NO 56.77 H [C H (NF 20.00 N .C H (NF 15.78 1.42 265 0.89 BOF 1 N 1'1 (B1'1 25.71 +HC1 v 1 NH C1O 43.51 +CO [C H (NF 15.00 +H +N .C H (NFZ)4 18.91 1.437 287 0.976 BOF+ :N 1'1 (B11 28.01 HCH- V1 NOCIO. 38.70 CO+ [CJlJNFQ- 15.00 H2+Ng 260 to 300 seconds, comprising 2 to 15 wt. percent bomu, 5 to wt. percent of a CNF oxidizer selected from the group consisting of tetrakis (difluoramino) butane and tetrakis (difluoramino) tetrahydrofuran, to 60 wt. percent of an oxygen oxidizer selected from the group consisting of nitronium perchlorate, hydrazinium nitroformate, hexanitroethane and ammonium perchlorate, and 5 to 30 wt. percent of a solid polymeric binder having the composition of polybutadiene (N F adducts represented by the recurring unit composition [C l-l (NF in which y represents 1.3 to 2 NF groups per recurring unit, the boron being in a 1:1 atomic ratio of fluorine in the composite to form BOF as a main combustion product.

rahydrofuran and the oxygen oxidizer is hydrazinium nitroformate.

4. A high-energy composite as defined in claim 1 in which the CNF oxidizer is tetrakis (difluoramino) butane and the oxygen oxidizer is ammonium perchlorate.

5. A high-energy composite which on ignition undergoes combustion to form BOF and CO as the main combustion products containing boron and oxygen present in the components of said composite, said composite containing 2 to 15 wt. percent boron, 5 to 25 wt. percent tetrakis (difluoramino) butane, 40 to 60 wt. percent nitronium perchlorate and 5 to 30 wt. percent polybutadiene (N 12) adduct as solid binder, said binder containing 1.3 to 2 N1 groups per 4 carbon atoms, the boron in the composite being in a 1:1 atomic ratio to fluorine in the composite to form BOF as a main combustion product and the nitronium perchlo- 2. A high-energy composite as defined in claim I in rate pp y oxygen to form the BOF and 

1. A HIGH-ENERGY COMPOSITE WHICH ON IGNITION BURNS AT A CONTROLLED RATE AT A SPECIFIC IMPULSE IN THE RANGE OF 260 TO 300 SECONDS, COMPRISING 2 TO 15 WT. PERCENT BORON, 5 TO 25 WT. PERCENT OF A CNF2 OXIDIZER SELECTED FROM THE GROUP CONSISTING OF TETRAKIS (DIFLUORAMINO) BUTANE AND TETRAKIS (DIFLUORAMINO) TETRAHYDROFURAN, 40 TO 60 WT. PERCENT OF AN OXYGEN OXIDIZER SELECTED FROM THE GROUP CONSISTING OF NITRONIUM PERCHLORATE, HYDRAZINUM NITROFORMATE, HEXANITROETHANE AND AMMONIUM PERCHLORATE, AND 5 TO 30 WT. PERCENT OF A SOLID POLYMERIC BINDER HAVING THE COMPOSITION OF POLYBUTADIENE (N2F4) ADDUCTS REPRESENTED BY THE RECURRING UNIT COMPOSITION (C4H6(NF2)Y) IN WHICH Y REPRESENTS 1.3 TO 2 NF2 GROUPS PER RECURRING UNIT, THE BORON BEING IN 1:1 ATOMIC RATIO OF FLUORINE IN THE COMPOSITE TO FORM BOF AS A MAIN COMBUSTION PRODUCT.
 2. A high-energy composite as defined in claim 1 in which the CNF2 oxidizer is tetrakis (difluoramino) butane and the oxygen oxidizer is hexanitroethane.
 3. A high-energy composite as defined in claim 1 in which the CNF2 oxidizer is tetrakis (difluoramino) tetrahydrofuran and the oxygen oxidizer is hydrazinium nitroformate.
 4. A high-energy composite as defined in claim 1 in which the CNF2 oxidizer is tetrakis (difluoramino) butane and the oxygen oxidizer is ammonium perchlorate.
 5. A high-energy composite which on ignition undergoes combustion to form BOF and CO as the main combustion products containing boron and oxygen present in the components of said composite, said composite containing 2 to 15 wt. percent boron, 5 to 25 wt. percent tetrakis (difluoramino) butane, 40 to 60 wt. percent nitronium perchlorate and 5 to 30 wt. percent polybutadiene (N2F4) adduct as solid binder, said binder containing 1.3 to 2 NF2 groups per 4 carbon atoms, the boron in the composite being in a 1:1 atomic ratio to fluorine in the composite to form BOF as a main combustion product and the nitronium perchlorate supplying oxygen to form the BOF and CO. 